1. Field of the Invention
The present invention relates to a compound useful as an intermediate in the preparation of a dye releasing redox compound which is suitable for use in the color diffusion transfer process and, more particularly, to a compound useful as an intermediate for producing a dye releasing redox compound having improved transferability, light fastness and hue.
2. Description of the Prior Art
Color diffusion transfer color image forming processes using a dye releasing redox compound are described in Japanese Patent Application (OPI) No. 104343/1976 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application"), U.S. Pat. Nos. 3,932,381, 3,943,987, 3,928,312, 3,931,144 and 3,954,476, and Research Disclosure, No. 13024 (1975). The term "dye releasing redox compound" refers to a compound in which a group referred to as the "redox moiety" and a dye (including a dye precursor) moiety are bonded. The redox moiety has attached thereto a ballast group which renders the redox compound immobile, but the redox moiety splits from the compound and releases a compound having a dye moiety upon redox reaction with the oxidized color developing agent under alkaline condition. That is, a light-sensitive element comprising a light-sensitive silver halide emulsion layer having associated therewith a redox compound is exposed to light and developed with an alkaline processing solution, whereby the redox compound per se is oxidized in proportion to the amount of developed silver halide and the compound splits into a compound having a dye moiety (hereinafter referred to as the "dye compound") and a non-diffusible quinone compound by means of the alkaline processing solution. As a result, the dye compound diffuses into an image receiving layer to provide a transferred image therein.
Examples of redox compounds which release yellow dyes are described in U.S. Pat. No. 3,928,312 and Research Disclosure, 13024 (1975). However, technical problems are accompanied using the dye releasing redox compound as specifically described in these publications. The stability of the transferred color images is not sufficient (for example, the light fastness of the images is not good and the color images fade to a large extent under light) and the transfer of dye compounds is not sufficient and the transfer speed of dye compounds is low.
In addition, improved yellow dye releasing redox compounds are described in U.S. Pat. No. 4,013,633. However, as a result of recent investigations, it has been learned that these redox compounds suffer a change in hue of the dye compounds depending on the pH of the system.
Examples of redox compounds which release magenta dyes are described in U.S. Pat. Nos. 3,932,380 and 3,931,144. However, using such dye releasing redox compounds as specifically described in these publications, technical problems are encountered. The stability of transferred color images is insufficient (for example, the light fastness of the color images is not good and the color images fade to a large extent under light) and the transfer of the dye compounds is not sufficient.
With respect to the fading-in-dark of transferred magenta dye images, it has been known that unreacted monomer (such as acrylic acid, butyl acrylate, etc.), when a polymer acid (for example, polyacrylic acid, a copolymer of acrylic acid and butyl acrylate, etc.) as disclosed in U.S. Pat. No. 3,362,819 is used for a neutralization layer, adversely influences the fading-in-dark of transferred dye images. It has also been found upon further investigations that unreacted butyl acrylate monomer, in particular, increases the fading-in-dark of the magenta dye image obtained from a method as described in the prior art, for example, U.S. Pat. No. 3,932,380. However, it is extremely difficult from a technical standpoint to limit the amount of unreacted monomer to such an extent that it does not adversely influence the light fastness of the image. Therefore, it has been desired to develop a redox compound which releases a dye compound which is less sensitive to such unreacted acid monomer.